Process for preparing lipid coated particles of plant material

ABSTRACT

The invention relates to methods for making completely biodegradable, hydrophobic, oleophilic plant based materials which are useful in adsorption of petroleum products. The materials have an average diameter of from 1 to 5 mm, and an ash content of from 10% to 30%. The non-paraffin coating is an animal fat product, preferably produced by dissolving a pure animal fat and using this as the coating material.

RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/893,653 filed May 14, 2013, which claims priority from U.S.Provisional Patent Application No. 61/714,906 filed Oct. 17, 2012,incorporated by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to completely biodegradable, hydrophobic,oleophilic plant based materials which are useful in adsorption of crudeoil, and other petroleum products, especially from spills in water. Moreparticularly, it relates to plant particles (date palm tree particles,e.g.), which have had their normally hydrophilic surfaces modified bynon-paraffin lipid materials, resulting in hydrophobic particles whichare oleophilic and selectively adsorb oil and repel water.

BACKGROUND AND PRIOR ART

Every day, tens of millions of barrels of oil are transported overbodies of water which are also important sources of food and drinkingwater to millions of people. Oil spills, of course, have a tremendousnegative impact on marine life, potable water, and create a “rippleeffect” in, e.g., the tourist industry, health care in affected areas,etc. As the world's demand for crude oil continues to grow, the need tohave effective remedies available to address oil spills quickly, andeffectively does as well.

Plant based materials are well known as oil adsorbing materials. Theirefficacy, however, is hindered when the oil material to be adsorbed iscombined with water. The chemical composition of plant materials is suchthat they are hydrophilic, and will adsorb water more readily thanpetroleum products. Further, when these plant materials adsorb water,they become heavy and sink.

There have been attempts made to use plant materials to remove oilspills. For example, see Banerjee, et al., Chemosphere, 64:1026-1031(2006); Sayed, et al., Desalination, 194:90-100 (2006); Annunciado, etal., Marine Pollution Bulletin, 50:1340-1346 (2005); Karakasi, et al.,Fuel, 89:3966-3970 (2010); and Carmody, et al., J. Colloid and InterfaceSci., 305:17-24 (2007). Annunciado and Banerjee are the most relevant ofthese, as they deal with plant materials for oil adsorption. U.S. Pat.No. 4,444,148 to Lander teaches coating plant materials with paraffin,to render them buoyant and hydrophobic. The invention disclosed herein,however, differs markedly from what is disclosed in the prior art. Inthe case of Banerjee et al., fatty acids are grafted onto plantmaterials, using H₂SO₄ as the catalyst, whereas the invention, as willbe seen herein, involves physical coating without the use of a graftingcatalyst. Further, the preferred coating materials of Banerjee et al.,are low molecular weight lipids which are liquid at room temperature, ascompared to the preferred materials of the invention, which are animalfats and solid at room temperature. Also, Banerjee et al. state thatparticles of 227 μm were the optimal size for oil adsorption. Experiencehas shown, however, that particles of this small size are not buoyant,and thus are not useful for removal of oil from bodies of water. Also,Annunciado states that smaller particles adsorb oil at a much lower ratethan do the particles of the invention.

There have been various additional approaches to the problem of removinghydrocarbon spilled as a result of various actions. U.S. Pat. No.5,492,881 to Diamond describes various products which can be used toabsorb hydrocarbon, such as oil. Cellulose materials are treated torender products hydrophobic and oleophilic. Options include theincorporation of microbes, a fire retardant, low ash content (1%), andincorporation of paraffin. Removal of spilled petroleum products usingbacteria is an inherently slow process because of the biologicalreaction. Such is not a feature of the present invention. U.S. Pat. No.4,072,794 to Tomita et al. coats fibers with paraffin, and also includeslatex in the composition. Latex is not biodegradable, in contrast to theinvention described herein.

International application WO 2012/136981 converts plant materials tocharcoal, with dimineralizing. Hence, natural, untreated plant materialsare not used.

U.S. Pat. No. 4,172,039 to Akiyama describes use of coir dust, i.e.,material from coconut fruit. Coir dust has different porosity from thematerials of the invention. The difference in composition requires theuse of a containment means in using the coir based product, in contrastto the invention described herein.

WO 1998/45018 describes a product based upon coconut palms, where nohydrophobic coating is utilized.

None of these references teach or suggest the invention described hereinand elaborated upon in the disclosure which follows.

SUMMARY OF THE INVENTION

The invention relates to plant materials, coated directly with lipidmaterials, to render them hydrophobic, and useful as adsorbents for oiland petroleum products, both in the presence of water, and when “dry.”

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention utilizes inexpensive materials, e.g., trimmings orother waste materials, from plant sources. Preferably, the plant sourceis the date palm tree. The trunks of date palm trees are composed oflarge amounts of lignocellulose, which is itself composed of lignin,cellulose, and hemi-celluloses. In turn, the building blocks of ligninare phenyl propanoid units, while hexoses and pentoses make up celluloseand hemi-cellulose. The biopolymers have strong affinity for watermolecules. When water attaches to these polymers via hydrogen bonding,the materials become very poor adsorbents for oil and other petroleumproducts.

The inventors have discovered, however, that when these plant materialswere coated with hydrophobic material, e.g., lipids dissolved from solidanimal fats, the resulting, coated particles lost their ability to formhydrogen bonds with water, and retained their ability to adsorb theaforementioned petroleum products. In addition, the resulting coatedparticles became, and remained buoyant, and thus can be removed veryeasily following their use as oil adsorbents.

The particles of the invention, as noted supra, are made from plantmaterials, preferably date palm tree derived materials, e.g., trimmingsor other waste products from the tree. These trimmings are referred toby one author as “petiole” or as “karab” in Arabic. See Agoudjil, etal., Energy and Buildings, 43:491-497 (2011), incorporated by reference.Alternatively, one may refer to the petioles of the tree; Material fromthe trunk are also preferred, although “karab” will be exemplifiedherein.

Once the karab is gathered, it is treated to remove any moisturetherefrom. Preferably, this is done by drying the material in an oven ata temperature sufficient to drive off the water, but insufficient todamage or to char the lignocellulose. Once dried, the material istreated to yield particles of the desired size. These may range fromabout 0.1 to about 10 mm; however, it has been found that producingparticles with an average diameter of less than 1 mm greatly increasesthe cost of manufacture, while also increasing the available surfacearea for oil adsorption. In balancing cost and surface area foradsorption, diameters of from 1-5 mm are preferred. The particlecompositions contain from about 10% to about 30% ash.

To elaborate, smaller sized particles expose more of the interior,porous portions of the particles to the crude oil, to facilitateabsorbency therein. The penetration of oil into the interior of largerparticles is much slower; however, smaller particles do tend to sinkwhen placed on water because of its high concentration of minerals suchas silica (Si) which have very high densities.

The size of the particles is important because by decreasing the averagediameter, the surface area of a given sample of particles increases,which facilitates oil uptake capacity.

Mixtures of particles in the preferred size range with other materials,e.g., particles outside of the preferred size range, as well as othermaterials, is of course possible, but in addition to the issuesdiscussed supra, it was observed, in experiments, that when a widerrange of particle sizes were used, adsorbency was not as efficient.Uncollected, residual oil remained, and additional adsorbent wasnecessary to remove it all.

Oil uptake results from capillary action, which is defined by anequation, viz.:H=2γ cos θ/ρgr

where ρ is fluid density, γ is surface tension of the fluid, θ is thecontact angle between the particle surface and the fluid, and r is thecapillary radius of the pore.

To explain further, the contact angle θ depends upon interaction betweenthe material surface, and fluid chemistry. If there is no coating on thesurface of the particles, oil and water compete for adsorption. If awater molecule contacts the surface first, the molecule enters a pore ofthe material, due to hydrogen bonding. Smaller contact angles (θ<90)between the water molecule and the unmodified particles helps water topenetrate the materials and be adsorbed thereby.

When a surface coating is placed on the particles, however, interfacialtension between the water molecules and exterior surface are altered,and both the pore diameters and contact angle increase significantly,with the latter now greater than 90°. Water molecules are thus preventedfrom entering, i.e., being adsorbed. In contrast, the hydrophobiccoating allows oil to enter selectively, a result of the hydrophobicityof the pores and an acute contact angle between the oil and theparticles. The pore spaces become filled with oil with no competitionfrom water.

This explanation was validated in experiments, where coated particles inaccordance with the invention were kept in water for several days, andneither adsorbed it, nor sank. The plant particles of the inventionremain buoyant even after adsorption of petroleum products, such ascrude oil.

The particles are coated with hydrophobic lipids, such as animal fatderived lipids. Pure lipids may be used as well as lipids extracted fromsolid animal fats. Many methods for extracting lipids from solid fatsare known, and need not be reiterated here. As shown in the exampleswhich follow, petroleum ether and hexane are especially preferredsolvents, but other straight or branched chain alkanes/aliphatics, suchas any C₆-C₁₂ alkane, or mixtures thereof, may be used.

1. The use of solvent extracted lipids is preferred, because when longchain, molecules, which are semi-solid in nature are used, even in pure,dissolved form, the process of coating the particles can result innon-homogeneous, non-uniform products, resulting from the uneven processof solidification during the coating. As is shown in the examples,infra, an advantage of using solvent extraction is the ability tocontrol the removal of the solvent, with pure uniform application of theextracted lipids.

The raw fat used may be any available animal fat. Bovine, ovine, andother source animals may be used.

While not wishing to be bound to any particular theory as to thefunctioning of the invention, studies have revealed that karab orpetiole from date palm trees contains high amounts of mineral residues,i.e., from 5-20%. These mineral residues are Si based, and maycontribute to the ability of the particles to adsorb oil and repelwater. Analysis of residual as a following combustion, showed theinformation on mineral content environmental electron microscopy/EnergyDispersive X-ray with (ESEM/EDX tests, both confirmed these findings.

Features of the invention will now be seen by way of the examples whichfollow.

EXAMPLE 1

This example describes the manufacture of the particles of theinvention. Date tree trimmings (referred to hereafter as “karab” or“petiole”) were collected, washed thoroughly, and then dried, overnight,at 105° C. After drying, the trimmings were chipped into smaller pieces,and then milled to achieve particles ranging from 1-5 mm in size. Theseparticles were then dried again, to remove any residual water.

Animal fat (sheep fat), was used as the source of the materials used tocoat the particles. Samples of the animal fat were placed in thethimbles of two different Soxhlet extractors with two different solventsand two parallel extractions were carried out. To elaborate, i.e.,either hexane or petroleum ether, was placed in a still pot of a Soxhletsetup, in a manner well known to one of ordinary skill in the art. Thisresulted in selected extraction of lipids from the solid animal fat,into the liquid solvents. This was continued for different lengths oftime (up to four hours) to obtain saturated solutions for optimumcoating.

Solvents into which fats were dissolved were separated from the twodifferent (parallel) Soxhlet extractions, and portions of theparticulate trimmings were mixed together with each of the solvents intwo different Rotavap vessels. Sufficient solvent was used to completelysubmerge the particles in two separate rotary evaporators (Rotavap)device. The materials were mixed this way so that particles could beuniformly coated, with the condenser of the device operating at a starttemperature below that of the boiling point of the solvent so as toavoid premature vaporization.

After a maximum mixing time of 20 minutes, the temperature in theRotavaps were raised, so as to evaporate the solvent as completely aspossible. Any residual solvent was removed via drying in an oven at atemperature above the solvent boiling point. If necessary all steps wererepeated.

Two samples resulted from two different Soxhlet extractions, i.e., onecoated with the fat substance dissolved in hexane, and the other coatedwith fat substances extracted into petroleum ether. It was observed thatthe particles coated with the hexane extract had a very strong,unpleasant odor, while those coated with the petroleum ether extract,did not.

In further experiments not elaborated upon herein, it was determinedthat branched fatty acids, such as 4-methyloctanoic acid 4-ethyloctanoicacid, and 4-methylnonanoic acid, are the cause of unpleasant odors inthe extracts. These branched fatty acids were extracted into n-hexane,but not petroleum ether.

The examples which follow describe experiments using the particlescoated with the petroleum ether extract; however, experiments were alsocarried out using the hexane extract. These particles functioned in thesame way the particles coated with the petroleum ether extract did, butwere less desirable due to the foul aroma associated with them.

EXAMPLE 2

The resulting coated particles were hydrophobic, which was shown byplacing 3 g of coated particles, and 3 g of uncoated particles, inseparate, equal portions of water. After ten minutes, the uncoatedparticles had adsorbed the water, while the coated particles did not.Also, they remained afloat with minimal or no adsorption of water.Similar tests were carried out with stirring of the water for fiveminutes. The results were promising. Similar experiments were carriedout for overnight in stagnant water to test water repellency. Thesetests also showed very encouraging results.

EXAMPLE 3

Comparative tests were then carried out where coated, and uncoatedparticles, were added to containers holding the same amounts of bothwater, and crude oil. As with Example 2, equal quantities of theparticles were added. Given their different densities, the crude oilfloated on top of the water in each sample.

The uncoated particles adsorbed the water and, to the extent any oil wasremoved, it was a result of disturbance when the particles were removedfrom the container. In contrast, the coated particles adsorbed no water,but instead selectively adsorbed the crude oil. When the coatedparticles were removed, essentially clean, crude oil free waterremained.

The foregoing examples set forth a method for preparing an oil adsorbentparticulate material, by dissolving a combining plant particulatematerial in a liquid form of a lipid or lipid mixture, under conditionsfavoring uniform coating of the particles with the lipid material. Theresulting coated particles provide an exemplary product for adsorbingpetroleum based products from, e.g., aqueous environments; however, theyfunction in both aqueous and non-aqueous environments.

The plant material particles preferably have a diameter of from about 1mm to about 5 mm, and are preferably from date palm trees. The petioleor karab of the date palm tree is the preferred source of the particles,but material such as waste from the tree trunks may also be used.

Preferably the lipids used to coat the particles are obtained bydissolving animal fats into a solvent, such as petroleum ether. Whilepure, liquid lipids may be used, it is preferred to use lipids dissolvedin a solvent because, upon evaporation of the solvent, the lipids coatthe particles more completely and evenly than pure lipids do. When thelipids are obtained from dissolved animal fats, the resulting productwill not be a “pure” lipid, but a mixture of different triglycerides.The skilled artisan recognizes that a triglyceride always contain aglycerol moiety, having bound there to three fatty acid molecules. Thesemolecules may be the same, or different. Fatty acid composition ofdifferent animal fats are well known, as evidenced by, e.g., Hilditch,et al, “Sheep Body Fats,” (1941), incorporated by reference. Generally,the fatty acids are saturated, and unsaturated hexadecanoic andoctadecanoic acids, such as palmitic, oleic, stearic, and linoleicacids. The compositions will vary from animal to animal, but thetriglyceride molecules will generally contain at least 50 and preferablyat least 55 carbon atoms. Also see Weber, et al, Fuel 94: 262-269(2012), incorporated by reference.

Referring back to the solvents, it has been observed that certainsolvents, e.g., n-hexane or other straight chain alkanes or aliphatics,dissolve branched lipids into the solvent. While these lipids functionin the manner described herein, their malodorous qualities makes themless desirable as coating agents for the particles.

In operation, the coated particles are simple to use: one simply deploysthem at a source where undesired petroleum products are present for atime sufficient for the particles to adsorb the petroleum products. Aswas shown, supra, the particles remain buoyant, and can be removed veryeasily, by standard methods well known to anyone involved in the field.

Further, in contrast to other systems, the compositions of the inventiondo not incorporate microbes which serve to biodegrade petroleumproducts. By relying on the oleophilic products of the invention, rapidremoval of hydrocarbons is possible, as compared to the slow pace atwhich bioreactions occur.

In one exemplary embodiment of the invention, particles in accordancewith the invention can be placed in a water repellant containment means,such as water repellant meshed nylon, or other appropriate fabrics, soas to provide miniature “booms” which can be used instead of freeparticles. Such booms” can provide a more efficient way of removing anypetroleum products from an aqueous environment.

It must be noted, however, that containment means are not required;rather they serve as a convenience to the user. The distinction isimportant because other plant based materials, due to their porosity andother facts must be placed in containment means, as they are notbuoyant.

Other embodiments of the invention will be clear to the skilled artisanand need not be listed herein.

It should be noted that the particles of the invention were tested andproved to be useful for adsorbing oil from non-aqueous environments aswell, such as simple spills on dry surfaces.

When used in an aqueous environment, the nature of the water was not afactor. Tests were carried out in both deionized, and sea water, as wellas stagnant and fresh water, and its performance was equivalent in allcases, as well as for different types of oil and petroleum products(e.g., Arab heavy, medium and light crude oil, emulsifier oil, and burntor used engine oil).

The terms and expression which have been employed are used as terms ofdescription and not of limitation, and there is no intention in the useof such terms and expression of excluding any equivalents of thefeatures shown and described or portions thereof, it being recognizedthat various modifications are possible within the scope of theinvention.

We claim:
 1. A process for preparing lipid coated particles of plantmaterial, comprising: (a) contacting a solid animal fat with petroleumether to extract lipids from the solid animal fat thereby forming amixture of petroleum ether and lipids, wherein the extracted lipids donot contain branched fatty acids; (b) admixing particles of a plantmaterial with said mixture, wherein said particles have an averagediameter of from about 1 mm to about 5 mm, an ash content of from10-30%, and from 5-20% silica based mineral residue and have been driedto remove any moisture therefrom; (c) coating said particles with saidlipids by removing said petroleum ether, and (d) drying the lipid coatedparticles to remove any remaining petroleum ether therefrom.
 2. Theprocess of claim 1, wherein said animal fat is sheep fat.
 3. The processof claim 2, wherein said plant material is petiole.
 4. The process ofclaim 1, wherein said plant material is from a date palm tree.